1. Field of the Invention
The present invention relates generally to a system and method for fumigating containerized cargo without the use of tarpaulin, and more particularly to such a system and method that utilizes a specially adapted portable containment door that creates a seal around the main opening of the shipping container and provides the necessary connection inlets and outlets for fumigant injection and sampling lines.
2. Description of Related Art
Containerization of cargo has revolutionized the shipping industry by increasing efficiency through the creation of standardized shipping containers that are designed for movement through all major modes of transportation, including cargo ships, trucks, and railroad cars. Due to such increases in efficiency, and improvement in refrigerated shipping container designs, a wide variety of products, are now shipped throughout the world. With an increase in the availability of a wide range of products, including perishable items, the risk of transporting harmful pests from one country to another along with the shipped goods also is enhanced. Foreign pests often have the potential of endangering indigenous agriculture and wildlife, thereby causing widespread problems within existing agriculture systems. As a result, a large number of transported cargo, particularly produce, must be fumigated upon arrival in certain destinations.
The standards of the method for fumigating cargo containers are established by the Plant Protection and Quarantine (PPQ) branch of the United States Department of Agriculture (USDA) and are detailed extensively. According to the current conventional method for the fumigation of containerized cargo, a tarpaulin is placed over the single container unit or multiple container units that are being fumigated. The cargo is arranged within the container in a manner such that the gas fumigant effectively circulates and penetrates the stored substances. A series of fans are introduced inside of the container, in order to create a flow of the fumigant. After the fans are placed, gas introduction lines are positioned behind the fans through the main rear doors of the container. At least three gas sampling tubes are placed in specific locations within the bulk containerized cargo and are used to actively monitor the concentration of the fumigant within the cargo during the fumigation process. The containers are typically large shipping containers, however, the tarpaulin method can be used with smaller containers.
Once the fans, sampling tubes, and introduction lines are positioned, one or more tarpaulins are simply draped over the cargo containers and sealed along the ground through either loose or wet sand, sand snakes, water snakes, weights, adhesives, or any other suitable sealing means. After the tarpaulin is sealed, the amount (typically by weight) of fumigant required is calculated based on the contained volume. Once the amount is determined, a gaseous fumigant, such as methyl bromide, is caused to flow through at least one introduction line into the contained volume and hence through the open doors of the tarpaulin covered shipping containers. The fumigant is allowed to flow into the tarpaulin confined space until calculated amount has been introduced. The fumigant concentration level is subsequently sampled, typically using three sampling tubes, to determine whether a predetermined concentration level has been achieved throughout the contained volume. If the concentration level is too low, then additional fumigant may be introduced. Conversely, if the concentration level is too high, then the fumigation time may be reduced. Upon completion of the fumigation phase, the volume is aerated through a method that is in accordance with treatment guidelines and/or the Fumigator's PPQ compliance requirements. The method of aeration typically involves placing fans and exhaust ducts underneath the tarpaulin so that the fumigant is evacuated into the atmosphere in a controlled manner. Once the container is sufficiently aerated, typically to less than 5.0 parts-per-million (5.0 ppm) for methyl bromide, the tarpaulin is removed, and the cargo is subsequently released.
There are many problems associated with using the tarpaulin method for fumigation containerized cargo. First, if performed outside of an enclosed environment, the tarpaulin method of fumigation can only be performed in certain weather conditions, specifically low wind situations. Also, the tarpaulin method is time consuming requiring the placement of a large tarpaulin. Furthermore, during placement and storage the tarpaulin can be damaged by the corners of the containers or other sharp objects, thereby leading to leaks. Finally, many problems have arisen related to the toxicity and ozone depletion characteristics of many used fumigants, especially methyl bromide. Tarpaulins are extremely difficult to completely seal off, leading to the inevitable release of fumigants during the fumigation process. Also the tarpaulin encases a much larger volume than just the container compartment, requiring the use of excess fumigant to adequately fumigate the contents of the cargo container. In turn this excess fumigant is still vented into the atmosphere during the aeration process, leading to greater environmental damage.
As a result of the numerous disadvantages present with the conventional tarpaulin fumigation method, the background art reveals at least one attempt directed to fumigation of containerized cargo without the use of tarpaulin. U.S. Pat. No. 6,403,027, issued to Napoles et al on Jun. 11, 2002 describes such a method for fumigating cargo containers without the use of a tarpaulin. That method, commonly generally described as a “tarpless fumigation method,” eliminates the need for a tarpaulin by using the cargo container as an enclosure for containing the fumigant during the fumigation process. The method includes placing fans and gas sampling tubes within the cargo container, and threading the electrical lines of the fans and the lines of the gas sampling tube out through a preexisting drain hole in the bottom of the cargo container. The gas introduction line is placed through another preexisting drain hole. The used drain holes are then sealed using a commercially available sealant, while the unused drain holes are plugged using any suitable means. Finally, after the main rear cargo doors are closed, the fumigant is flowed into the cargo container, and the contents of the cargo container are subsequently fumigated. While the method disclosed by Napoles reduces the amount of space that must be filled with fumigant, it is still prone to leaks. Specifically, it has been found that the main rear doors on a large number of shipping containers, particularly older containers, are damaged, not airtight, or otherwise incapable of maintaining an adequate seal thereby leading to the fumigant leakage from the container directly into the surrounding atmosphere.
There therefore exists a need for an apparatus and method for fumigating containerized cargo that does not utilize a tarpaulin and is both installable and operated in a quick and easy manner. Furthermore, this system must minimize the amount of fumigant that is used and limit the amount of fumigant that leaks out during the fumigation process.